I'm developing on my ubuntu 9.10 machine for the web (php).
I'm using it sendmail for sending mails, and while developing on my local machine, I send local mails (to my user 'doron').

Up until a few days ago, I was able to send mails both from php's mail() function, and from the command line using the mail command.
I'm using sendmail with mailutils.

Since the last few days, it seems like it stopped working.
When I try to send mail from the command line, I get the following in my syslog (and mail.info, and mail.log):

Mar  3 13:27:58 doron-desktop sendmail[4693]: o23BRwlA004693: from=doron, size=84, class=0, nrcpts=1, msgid=<201003031127.o23BRwlA004693@doron-desktop.>, relay=doron@localhost
Mar  3 13:27:58 doron-desktop sm-mta[4694]: o23BRwtQ004694: ruleset=check_rcpt, arg1=<doron@doron-desktop>, relay=localhost [127.0.0.1], reject=553 5.1.8 <doron@doron-desktop>... Domain of sender address doron@doron-desktop does not exist
Mar  3 13:27:58 doron-desktop sendmail[4693]: o23BRwlA004693: to=<doron@doron-desktop>, ctladdr=doron (1000/1000), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30084, relay=[127.0.0.1] [127.0.0.1], dsn=5.1.8, stat=User unknown
Mar  3 13:27:58 doron-desktop sm-mta[4694]: o23BRwtQ004694: from=<doron@doron-desktop>, size=84, class=0, nrcpts=0, proto=ESMTP, daemon=MTA-v4, relay=localhost [127.0.0.1]

Trying to telnet locally to port 25 results in the following (same output for doron@doron-desktop):

doron@doron-desktop:/var/mail$ telnet localhost 25
Trying ::1...
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 doron-desktop. ESMTP Sendmail 8.14.3/8.14.3/Debian-9ubuntu1; Wed, 3 Mar 2010 13:26:06 +0200; (No UCE/UBE) logging access from: localhost(OK)-localhost [127.0.0.1]
helo localhost
250 doron-desktop. Hello localhost [127.0.0.1], pleased to meet you
mail from: doron@localhost
250 2.1.0 doron@localhost... Sender ok
rcpt to: root@localhost
553 5.1.8 root@localhost... Domain of sender address doron@doron-desktop does not exist

However - if I do the same, but use [email protected] in the mail from field, I get:

250 2.1.5 root... Recipient ok

My /etc/hosts file:

127.0.0.1       localhost
127.0.1.1       doron-desktop doron-desktop.

(If I don't have the "doron-desktop." (with the ending dot), the mail command takes a lot of time (around 30 seconds) until it responds, but the results are the same.)